The invention relates particularly to an air release valve of a type that can be used in conjunction with a water pipe line. It is known in relation to a water pipeline that it is often required to purge the pipeline of air present therein. Such air particularly may be present within the pipeline before water flow through the pipeline is initiated, i.e. when the pipeline is empty. Also, during flow of water through the pipeline, air in suspension in the water and pockets of air in the pipeline may collect in certain regions of the pipeline, typically peak regions and certain substantially flat sections.
An air release valve that provides for the release of air from a water pipeline, in its simplest form, includes an elongate valve body that defines a passage therethrough, along a longitudinal axis thereof that leads from an inlet end to an outlet end. The valve body is operatively mounted on a pipeline, particularly so that the inlet end of the passage communicates with the pipeline and the passage itself is substantially vertically disposed and leads upwardly to the outlet end thereof. The valve body defines a valve seat at the outlet end of the passage. The valve also includes a valve closure arrangement within the passage, the arrangement including a float that serves as a valve closure also. The float is axially displaceable within the passage defined by the valve body, particularly between a closed position, in which it seats against the valve seat, and variable open positions, in which it is spaced from the valve seat to expose the valve outlet. The open positions of the float are below its closed position.
In relation to a water pipeline having an air release valve of the above type mounted thereon in a suitable location for the release of air from the pipeline, in an initial condition of the pipeline, it is devoid of water and filled with air at substantially atmospheric pressure. In this initial condition the float is in an open position. When water is pumped into the pipeline, upstream of the valve, the advancing water pressurises the air in the pipeline downstream of the water. Air then initially passes through the air release valve, particularly past the float via a flow passage defined between the float and the surrounding valve body, the air escaping via the outlet of the valve body to the atmosphere. The air flow past the float may create a low pressure region above the float such as to cause it to be abruptly lifted into its closed position, thereby abruptly closing the valve outlet. Such closing of an air release valve is sometimes referred to as “premature closing” and may cause water hammer in the associated pipeline. Should the float not be lifted into its closed position under such air flow, water entering into the passage defined within the valve body, when air release is being completed, will induce upward displacement of the float, particularly until it reaches its closed position when air release is at least substantially complete. Such closure of the valve can occur abruptly and again may cause water hammer in the pipeline.
Insofar as further elements of an air release valve of the above and similar types are well known, they are not described in further detail herein.
Water hammer as may occur in conjunction with the use of an air release valve of the above type may result in damage to a pipeline, e.g. a burst. As such, it has been an object to provide an air release valve in conjunction with the use of which, the problem of water hammer is at least ameliorated.
A known new valve closure arrangement for use in an air release valve of the above type provides for a float and a valve closure that are displaceable towards and away from each other between an abutting position and variable spaced apart positions. In the abutting position, abutment particularly occurs within an area which is small, compared to the maximum cross-sectional area of the float in a horizontal plane, so that substantially the entire top surface of the float is exposed to the fluid pressure in the passage in the valve. The closure itself is biased downwards by gravity, i.e. to open. An upper limit position of the float is thus defined when the valve closure is in its closed position and the float abuts against the closure. The float is displaceable between this upper limit position and a lower limit position, through a range of intermediate positions. Also, an air flow passage is defined between the operative top and bottom of the closure, the passage having an inlet within the said area within which abutment occurs between the float and the closure, and an outlet that communicates with the atmosphere. With the float abutting against the closure, the air flow passage defined through the closure is blocked-off by the float. With the float spaced apart from the closure, the air flow passage is open. Insofar as the features of this new closure arrangement also are known, they are not described in future detail herein.
Although use of this known new valve closure arrangement within an air release valve has been advantageous, a solution to the water hammer problems was not achieved and it is thus an object of this invention to at least ameliorate the water hammer problems.